Unless they start yellowing or stunting it's probably just leaf roll, which is just a physiological response to environmental stressors. Could be too hot, too cold, or over/underwatering. If it's a temp thing, it should resolve on its own and shouldn't cause any permanent damage.
If it has been a little cool where you live (or the soil is too wet), it will resolve when the temperatures rise (or vice versa if it's been hot).
Edit: Based on your comment below, I'm guessing this is a result of the heat. Consider shading them.